I agree with Sage, I don't think he hates America or American cars as much as he claims he does. I don't think he likes American cars on our roads mind, but re-watch that TopGear episode where they had a road trip through part of America and Clarkson was in that old Camaro, he really enjoyed that experience and that car, ofcourse at the end of the show he says something along the lines of "two things we've learned from this. One, it's not as easy to buy a car as rent one, and two, don't go to America." Yet there he really liked that battered old Camaro.
The bottom line is that the majority of America cars work far better in America than they do over here and that magnifies his anti-American person and the jokes that result from it. Don't get me wrong, he doesn't particularly liek America, but the whole verbally tearing down everything in the way of American auto's is far more of an act than a true representation of Clarkson himself. Another example, the two Corvette tests, okay he genuinely didn't like the Z06 on the roads, neither did all of out magazines, but he really likes it on the track and he likes the C6 on the track and the orads, but he still poked fun at the suspension and the plastic bodywork even though he admitted that the car handled well and that he liked it. He liked the C6 so much that in a non-TopGear related column he said that despite it beingh lhd he would consider it as an option if he was in the market for a £50k sportscar.
And yes, he is actually a pretty smart, man. He plays that down a lot in the public spotlight especially on TopGear, he loves his image and playing that part as he's shown in TopGear, I think that he is genuinely over opinionated though.